The area known as bioprocessing relates to the characterization, expression and purification of biomolecules. In the purification of biomolecules, chromatography is still used as at least one step in almost all processes approved by the authorities for the manufacture of a biomolecule, such as a drug or a vaccine. A common feature for all the different principles of chromatography, such as affinity chromatography, ion exchange chromatography, hydrophobic interaction chromatography and multimode chromatography is that a number of operating variables—or quality measures—are available to design and optimise efficient processing.
Design of Experiments (DoE) is a commonly applied technique for planning and analyzing experiments, allowing the use of a minimum number of experiments, in which you can systematically vary several experimental parameters simultaneously and capturing as much information as possible. In general usage, design of experiments (DoE) or experimental design is the design of any information-gathering exercises where variation is present, whether under the full control of the experimenter or not. In the design of experiments, the experimenter is often interested in the effect of some process or intervention on some objects. Design of experiments is thus a discipline that has very broad application across all the natural and social sciences and engineering, but which has proved suitable to apply in bioprocessing.
Commercial products are available for using DoE in the optimization of chromatography conditions. For example, the AKTA™ avant 25 system (GE Healthcare, www.gelifesciences.com) has been used with the Design of Experiments (DoE) functionality of the UNICORN™ 6 control software (GE Healthcare, www.gelifesciences.com) to perform a DoE of loading and elution conditions resulting in a strategy for process development and scale-up of a recombinant protein purification (GE Healthcare, www.gelifesciences.com, Application Note 28-9827-80 AA). Even if the DoE helps reducing the number of experiments, with this approach one will still need to do experiments representative for the full range of each variable, resulting in a relatively large number of experiments, which of course require time and resource.
PreDictor RoboColumn™ units, which are commercially available prepacked, miniaturized columns that support high throughput process development (HTPD) may be used for DoE with a robotic liquid handling workstation, such as Freedom Evo™ (Tecan) for parallel chromatographic separations. Up to eight different conditions may be tested. However, as a pressure fall may appear when the needle of the robot leaves the column to re-fill liquid, the flow rate may not be totally constant. As the volumes of collected fractions are unknown, they will have to be determined experimentally.
EP 2 269 055 (Björkesten et al: “Preparation of liquid mixtures”) relates to a method of generating a liquid mixture of controlled pH and ionic strength, as well as to an apparatus applicable in such a method. One aspect of EP 2 269 055 is to provide a method of precise and accurate control of the pH and ionic strength of a liquid mixture. In brief, this may be achieved by providing a method of preparing a liquid mixture, such as a buffer, which method takes into account both the size and charge of organic as well as inorganic ions. A further object of EP 2 269 055 is to provide an improved method of buffer preparation, wherein the exact composition is first calculated and the buffer is subsequently prepared in a single step. A specific aspect of EP 2 269 055 is to provide the tools for buffer preparation wherein there is a guaranteed pH range for each respective buffer by calculation of the buffer capacity.
However, there is still a need in the bioprocessing area of faster ways of optimizing the conditions for separation of a selected biomolecule from a complex solution, such as antibodies from a liquid originating directly from a liquid cell culture, or from upstream processing of a liquid cell culture.